Calcium-dependent release of neurotransmitters is a crucial step in virtually all aspects of central and peripheral neuron function. The study of transmitter release has been limited, however, by the lack of suitable experimental preparations. Last year we reported the first recording of calcium currents in a vertebrate presynaptic nerve terminal using the calyx synapse of the chick ciliary ganglion. We have extended this study by modifying this technique to allow the recording of presynaptic calcium currents at the single channel level. These channels have a single channel conductance in the 13 pS range, and can be highly clustered. This report is the first description of calcium channel properties at the single channel level at any presynaptic nerve terminal. We will use this presynaptic nerve terminal preparation to search for other presynaptic ion channel types, both ligand-and voltage-gated. In addition, we are developing a technique to carry out patch-clamp recordings from a mammalian central nervous system presynaptic nerve terminal, i.e., the mossy fiber terminal in the hippocampus.